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Battling Battery Boats

Any submarine has the potential to cause trouble, but the myth of diesel-electric submarine invincibility in the littorals can be shattered if antisubmarine warfare skills are learned and practiced.

Most naval officers today view the diesel-electric submarine in shallow waters as an almost invincible adversary. This impression arises not from analysis or experience but from simple ignorance. Lack of theory and practice has perpetuated this myth, even in the face of advances in almost every area of submarine and antisubmarine warfare (ASW) technology. 1

Other than some in the submarine and maritime patrol air communities, few officers on active duty have practiced against actual submarines, and the number of officers and the time engaged are declining as other post-Cold War missions take precedence over the development of ASW skills. Operations against submarines in shallow waters always have been a rare occurrence, practiced for short periods by persons with little experience, resulting in frustration and failure. It is in this atmosphere that the legend of the battery-driven submarine in shallow waters has grown, fanned by the pro-ASW budget advocates and intelligence officers anxious to provide a maritime threat.

Any submarine has the potential to cause serious trouble. This indictment of ASW expertise should not lessen our recognition that submarines and mines are the only current threat to U.S. naval dominance. Long the weapon of choice for inferior sea powers, a submarine of any variety can delay and perhaps even thwart the efforts of a superior naval power.

Despite being potentially dangerous and difficult to locate, however, the battery-driven submarine has severe limitations—short endurance, low speed, small sensor apertures, few weapons, minuscule antennas operating in easily exploitable frequencies, cumbersome command-and-control arrangements, and questionable crew competence and confidence—that antisubmarine forces can exploit. The most important of these are those related to endurance. Battery capacity is so dominant an operational consideration that it dwarfs all other concerns.

Those without experience in or against conventional submarines have difficulty grasping the pervasive nature of this concern over the battery's charge, how it drives every decision on board the submarine, and how it can be used by the hunters. 2 For the captain of a battery-powered submarine, every tactical decision is based on the battery—how much energy is left, where the ship can go with that and how fast, how long before the battery ought to be or must be recharged, where the ship should be when the charging evolution takes place, how the weather and sea state will affect charging and detectability, and more.

The chief drain on the battery is propulsion. As in all marine propulsion, the relationship between energy and speed is not linear; the faster the submarine goes, the shorter the time between required rechargings. A submarine sprinting (16 knots) covers much less distance on a given battery capacity than the same boat operating at moderate speeds (6 knots). Unlike nuclear submarines, a battery boat has a very difficult time clearing datum in the face of modern ASW sensors: so avoiding detection is an order of magnitude more important.

Always influencing the boat's movements is the knowledge that time will have to be spent at periscope depth to charge, with masts constantly exposed. Deaf and cyclopean, the submarine will be vulnerable to visual and radar detection while charging generates the audio signals that compromise stealth.

The foremost virtue in ASW—especially in battling battery boats—is patience. The hunter must watch and wait, but with the surety that the battery-driven submarine eventually must show itself. Opportunities for detection can be created if the hunter can force the submarine to move, either to accomplish its mission or to avoid detection and prosecution. Moving far or fast decreases the time between charging evolutions and/or increases their length. A submarine charging one hour out of every twenty-four when operating at three knots will have to charge eight hours out of twenty-four if its speed is doubled to six knots.

Air independent propulsion (AIP) does little to offset these mobility difficulties. While operating, both Sterling and closed-cycle engines make the submarine more vulnerable to sonar detection. Even when sound mounted, closed-cycle engines radiate high structure-borne noise, the chief compromiser of underwater stealth. 3 Limited by the supply of stored oxygen, AIP devices are not sources of long-term energy, and their power output is much less than that of the battery. AIP may add to stealth by prolonging the time between mast exposures, but it does not add significantly to mobility.

Because of their short legs, battery-powered submarines have been likened to "mobile minefields," and like minefields, they can be avoided if their general location is known. Simply remaining well clear of a battery-powered submarine's general operating area frustrates the submarine and makes further ASW unnecessary. This is not as difficult as it may appear. Because the world fleet of submarines is relatively small, the number and characteristics of opposing submarines can be gauged fairly accurately. National sensors can report the number of submarines in port, making it easy to extrapolate how many might be present in a operating area. The command-and-control complexities imposed by communications limitations and the need to prevent mutual interference force submarines to operate singly or perhaps partnered in some proximity. Submarines never come by the dozen, even if the enemy has lots of them.

These limitations allow submarine hunters to use tactics that would be ineffective or dangerous against nuclear-powered opponents. An area searched for 36 to 48 hours without a detection is unlikely to contain a battery-powered submarine. If one is present, its remaining battery capacity would be so low that the chance of movement for anything but self-defense would be remote. The size of this "sanitized" area is determined by the forces available for the search and the ocean's environment. Several thousand square miles is not unreasonable for maritime patrol aircraft or towed-array sonars. Once such a space has been determined to be clear, the ships to be defended can occupy it in relative safety while the search is extended to a new area. When this new space has been cleared, the ships can move again. The distances in this kind of maneuver can be made large enough that the battery-powered submarine would have to move further and faster than can be done stealthily.

Once detected, a battery-driven submarine can be avoided by remaining well clear of datum. Short legs prevent the battery boat from closing distant contacts in a reasonable time, and the limits of battery capacity force it to snorkel often and long in order to pursue and close. Such a pursuit increases the probability of detection, eases localization, and promotes successful attack. These limitations, plus the realization that where one submarine is, there is unlikely to be another, allow ASW forces to concentrate resources on any suspected contact. Once it is located, persistent attacks render the submarine ineffective even if undamaged; only very experienced and courageous submariners can be effective in attack or counterattack while being pursued.

Long-term wide-area search operations are more effective today than ever before, not only because sensors are better but also because computers enable search efforts to be analyzed as they happen. Modeling the search by recording the time, position, and probability of detection for each sensor allows calculation of the probability of submarine location. ASW forces can search areas faster than battery-powered submarines can move. Searches managed on this premise permit ASW forces to reduce the possible areas of their opponents' positions such that, over time, detection and localization approach certainty.

Submarines are limited in available sensors. Battery-powered submarines, particularly small ones, lack the space, power, and people needed to employ towed arrays effectively and the space to mount the large hydrophones needed for long-range detection and localization. Radar—which has not been a useful tool for 40 years—generally provides more information to the enemy than to the user. In this realm, the periscope is valuable beyond all comprehension of a non-submariner. It is the only unambiguous sensor available to the submariner; but it is also a source of unambiguous detection for surface and air submarine hunters.

This has several effects. First, in submarine operations the desire to look exceeds that in all other human activities, except perhaps poker. This urge grows exponentially with uncertainty. The more inexperienced the captain, the greater the itch. The well trained and practiced can take a good look in six to ten seconds, but most spend half a minute or more. Visual detection during these scope exposures occurs more often than unpracticed forces realize. Among the most cost-effective ASW training is having lookouts and aircraft personnel observe submarine masts at sea at various speeds in long and short exposures. Once so trained, the eye is very effective—if undervalued.

Shallow water is a dubious haven for submarines and not one sought by submariners. In very shallow water, the thermocline is small or absent, so there is no roof under which to hide from sonars in the surface duct or across which to evade sonobouys. The bottom is an ever-present source of concern—grounding can ruin the whole day. If the hunters are seaward, the submarine is trapped against the beach. Maneuver, already limited by battery capacity, is constrained to less than 180deg. Out to 50 fathoms or so, the bottom and surface form a superb sound channel. This channel may be full of noise from the beach, surf, and inshore engines, but if the bottom is hard and the surface not too choppy, sound propagation is better than in most surface ducts. Snorkeling in such a duct with the listening device to seaward is almost sure to result in detection, and if aircraft are available, quick localization.

Foremost among the reasons that finding a submarine in shallow waters is seen as monumentally difficult is the improper operation of active sonar. Echo-ranging functions differently in this environment than in the deep ocean. Proper operation of sonars is a function of the training and experience of the sonarmen. Officers rarely understand the nature of the environment or the limitations of their equipment. Rotated through assignments too quickly to gain any real expertise, they remain near the bottom of the learning curve. Even well-trained and experienced sonarmen tend to turn up the power when the target-echo fades or is ambiguous. In reverberation-limited environments, that is exactly the wrong move. In shallow waters, turning down the power level and adjusting the pulse characteristics to roll a long sound wave up the slope of the bottom makes a submarine in this duct a fish in a barrel.

Searching with active sonar usually is unproductive. Regardless of its effectiveness, however, echo-ranging complicates the hunted submarine's decision making. When the searcher varies his pulse characteristics, keying intervals, and power levels randomly during the search, changes made on detection provide no intelligence to the hunted submarine. In addition, every change causes the hunted to question why and to ponder the probability of detection. For those with little experience, whose confidence may be low, such tactics encourage the tendency to lay low and await developments. Submarines hiding are not submarines attacking.

Once a submarine is detected, no ASW platform is more feared than the helicopter. When contact is made and three or more helicopters are employed, not even the fastest nuclear submarine can escape the net, unless the helicopters make a serious mistake. Against a battery-powered submarine, a single helicopter generally is enough. In shallow waters, the cheapest weapon can be delivered with precision against a target with the limited mobility of a battery-driven submarine.

"Torpedo in the Water" raises the pucker factor on any submarine to maximum tautness. No matter where the weapon is, or how inaccurately it is placed, it takes time to determine whether the torpedo is aimed at the submarine and if so, how well. The evasion tactics available to a battery boat at this point are hunker down and pray. Urgent attacks—putting a weapon in the water without knowing precisely where to aim it—will give pause to the most hardened or experienced submariner and may flush the unskilled or faint of heart.

The crew's skill and confidence in operating their submarine counts for much in determining the difficulty of the hunters' job and the efficacy of urgent attacks. Possessing a weapon system does not equate to operating it effectively. The more complex the system and the more demanding the environment, the more training, practice, and expertise a crew will need to employ it well. Adding to the submarine's inherent technical complexity is the paucity of clues about the outside world and the constant presence of high pressure water on all sides. Submarines—essentially, ships that sink intentionally—are stressful work places as a matter of routine. When they are being pursued by people who might be or are shooting at them, they become barrels full of very high stress. The captain's personal skill and courage, the officers' teamwork, and the crew's confidence in its captain and in themselves—all products of their culture, tradition, and training—need to be uniformly high if the boat is going to operate effectively. This is not easy to achieve.

There are no submarine crews at sea today who have been depth charged. No matter what the courage and discipline of these crews and the skill of their captains, when they are first engaged in combat, stress fractures will be high and failures often and complete. This is true for any group, but the magnitude of failure in submarines will be serious—with those less practiced likely to fail first. This environment was responsible for the large number of U.S. submarine commanders relieved in the year after Pearl Harbor for poor performance.

Achieving needed competence and sophistication in a small submarine force or in a country without a naval tradition is difficult. Possession of submarines does not translate into a submarine force. Thus, ASW is not an unbounded problem—particularly when facing battery boats. In a serious crisis, those with the most severe ASW problems will be the enemy submarines that will have to operate in the teeth of the U.S. submarine threat. The captains and crews of foreign boats are well aware of the magnitude of this threat; experience has shown that they may not even leave port.

None of this is new. Successful combined arms operations against battery-powered submarines were the norm when Task Force Alpha operated in the Atlantic in the late 1960s. 4 Antisubmarine exercises in RimPac and related efforts in the 1970s were very successful against a mix of nuclear- and battery-powered ships. Soviet battery boats were hunted to exhaustion in the 1960s and 1970s. But the knowledge and skills that created these successes seem to have faded in the post-Cold War environment.

ASW is a personal-skill-intensive activity, a team effort that prospers when combined arms are brought to bear intelligently. Modeling and simulation bring tools not available heretofore, but they cannot substitute for command interest and real experience at sea. Understanding geographic and environmental constraints and appreciating the significance of time—nothing in ASW happens quickly—are not lessons learned in classrooms or from the written page. They have to be gained through practice—in any operating staff that would like to consider itself competent in ASW, on every ASW ship and aircraft, relearned after every change of command, from mission commander to leading sonarman, and in every environment in which the ASW platform operates.

This is a demanding prescription. In today's world, the time and opportunities required to develop the needed skills are not likely to be considered worthwhile until after the first ship is sunk during hostilities or when a task force enters into contested waters.

The U.S. Navy appears to be becoming peopled by those who have the name of the business without the full ability to practice it. One solution to this demonstrated ignorance should be to limit assignment in any ASW leadership role to those officers who have had more than a hundred hours experience in contact with an opposing submarine. It would be interesting to see how many officers of what grade and warfare specialties could meet even this minimal test.

Perhaps a solution lies in specialization. Circumstances may not permit the whole fleet to become proficient, but a command-and-control cadre for ASW could be maintained and selected units—air, surface, and submarine—exercised together in depth for a month or so once a year. Then when the need arose, these forces could be dispatched to clear the way for strike, amphibious, and logistics units.

When ASW is learned and practiced, the battery boat hasn't a chance. To reverse Joe Louis's famous aphorism, "He can hide, but he can't run."